This invention relates generally to a system for transporting or storing semisolid materials, such as grease or ground or comminuted food products, and fluid materials, such as oil, in bulk quantities, and more particularly to a tank adapted for quickly and efficiently unloading semisolid or fluid material contained therein.
Coassigned U.S. Pat. No. 3,828,988 discloses an earlier tank for bulk transport and storage of semisolid materials. This tank has a follower piston with extruded or molded flexible neoprene seals at each end thereof for sealing the piston relative to the tank while accommodating changes in internal cross-section of the tank (variations of as much as 1/4 in. (8 mm) in diameter), and spring-biased nylon rollers for preventing canting of the piston as it moves within the tank. Although this tank performs well, and the neoprene seals provide an effective wiping action of the tank interior, thin smears or patches of grease sometimes remain on the inside surface of the tank after evacuation. While this is satisfactory for many purposes, it is not acceptable for all purposes, e.g., where the tank is to be loaded with a different type of grease after unloading and contamination of the second type of grease with the former type is not permissable, or where the tank is to.be loaded with comminuted food products. Also, the earlier tank follower has numerous parts and is relatively costly to fabricate and somewhat difficult to assemble and insert into the tank.
Heretofore, ground food products have not commonly been transported in bulk due to the difficulty or impossibility of maintaining a high standard of cleanliness and sterility in a transport tank. In lieu of bulk transport, other, less desirable, forms of transport have been used. These methods of transport typically have been expensive and time consuming. For example, in the processing of chicken, raw backs and wings are conventionally ground and transported several hundred miles for processing into frankfurters, lunch meat, etc. by packing the product into 55 gal. drums having plastic liners and transporting the drums in refrigerated trucks. Bulk transport of such material has been impractical because it has been too difficult to load and unload large tanks with the product and to sterilize the tanks, due, in part, to the excessive time involved in doing so.
Bulk transport of transformer oil, on the other hand, has not been uncommon, but because of the sensitivity of the oil to water and humid air, it has been very troublesome. Transformer oil may only be loaded into and unloaded from conventional tank trucks during conditions of low humidity and dryers must be installed on the truck to permit venting only of dry air. Because transformer oil must be kept absolutely dry, transformer oil should be totally sealed from ambient air when it is loaded, transported, and unloaded so that it can be transported regardless of weather conditions.